Science Scoops: Lobsters Know the Way

by Stephen James O'Meara

Only a few species of animals are known to have “true navigation” — meaning that they can find their way home even if transported to a totally different and unfamiliar environment. Most vertebrates are thought to be true navigators, but vertebrates make up only about one percent of all known living species. To date, only one species of “spineless” wonders (invertebrates) have been shown to be capable of true navigation, the Caribbean spiny lobster, Panulirus argus.

For most of the year, spiny lobsters spend daylight hours inside coral reef crevices, emerging at night to feed over considerable areas before returning in nearly total darkness to the same den. Spiny lobsters also show a remarkable ability to keep a constant course while migrating under water and to find their way even in darkness. Now researchers have discovered that they can also return to their feeding grounds after being displaced by some 12 to 37 kilometers.

How do the lobsters navigate so well?

To test a theory that spiny lobsters have a well-developed magnetic map sense, Larry Boles and Kenneth Lohmann (Department of Biology, University of North Carolina, Chapel Hill) captured lobsters, which they then relocated — some to the north of the capture site and some to the south.

The result?

The lobsters relocated north of the capture site immediately oriented themselves southward, whereas those relocated south of the capture site oriented themselves northward. When instead of transporting the lobsters, the investigators simulated the values of the magnetic field that would be encountered at northern and southern sites, the lobsters showed the same responses. So true navigation in spiny lobsters, and perhaps in other animals, is based on a remarkable “magnetic map sense” similar to that found in newts and thought to play a role in the long-distance movements of other vertebrates such as sea turtles and migratory birds.

Vocabulary

invertebrate: An animal that has no backbone. Worms, clams, insects, and lobsters are invertebrates.

magnetic map sense: The use of the Earth's magnetic field as a way to know a position and navigate to a new position.

simulated: Imitated.

vertebrate: Any of a large group of animals that have a backbone. Fish, amphibians, reptiles, birds, and mammals are vertebrates.

Activity

After the lobsters had been moved, how do scientists think they navigated, or found their way, back home?[anno: The lobsters responded to the Earth's magnetic field and used the field to navigate back to their homes.]

Why did the scientists simulate a magnetic field for the lobsters?[anno: They wanted to test their hypothesis that lobsters used the magnetic field to navigate.]

What is one way that humans do use the Earth's magnetic field to navigate?[anno: Answers may vary but could include the use of the magnetic compass.]